Refugees and migrants reach the Greek island of Lesbos after crossing the Aegean sea from Turkey.
Photograph: Aris Messinis/AFP/Getty Images

Europe’s deep divide over immigration is to be laid bare at an EU summit in Brussels on Thursday, with German chancellor Angela Merkel struggling to salvage her open-door policy while a growing number of countries move to seal borders to newcomers along the Balkan routes.

A debate on the migration crisis over dinner on Thursday evening will do little to resolve the differences, senior EU officials predict. Donald Tusk, the president of the European council, has avoided putting any new decisions on the agenda in an attempt to avoid fresh arguments.

The leaders of four anti-immigration eastern European countries met in Prague on Monday and demanded alternative EU policies by next month. Their plan amounts to exporting Hungary’s zero-immigration razor-wire model to the Balkans, sealing Macedonia’s border with northern Greece, and bottling up the vast numbers of refugees in Greece unless they are deported back to Turkey.

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Merkel had been due to lead a rival meeting of leaders of 10 countries on Thursday in an attempt to invigorate a pact with Turkey, but that has been called off following the bomb attack in Ankara on Wednesday.

Merkel’s plan – trading money and refugee quotas for Ankara’s efforts to minimise the numbers crossing the Aegean to Greece – hinges on EU countries volunteering to take in quotas of refugees directly from Turkey. But even among her allies – a so-called coalition of the willing – support for the policy is fading. Austria has announced stiffer national border controls this week, saying on Wednesday that it would limit the number of migrants it let in to 3,200 a day from Friday. “We must apply the brakes step by step,” interior minister Johanna Mikl-Leitner told reporters.

Vienna has also told Brussels and Balkan governments that it could close its borders within weeks. France, another member of the coalition, announced that it would not participate in any new quotas system.

“You can’t have 20 [EU] countries refusing to take in refugees,” said a European commissioner. But senior officials in Brussels admit that there is now a solid majority of EU states opposing Merkel.

In a pre-summit statement to parliament in Berlin on Wednesday, Merkel stoutly defended the policies that are under fire at home and across Europe. Despite the problems, she said, 90% of Germans continued to support taking in people fleeing war, terror and persecution. “I think that’s wonderful,” Merkel said.

Her speech dwelt overwhelmingly on the faltering pact with Turkey, struck in November. Ahmet Davutoglu, the Turkish prime minister, was to attend the mini-summit in Brussels, but cancelled his trip on Wednesday following an apparent terror attack in Ankara. The issue at the EU summit, Merkel said, will be whether to press ahead with the Turkey pact or whether to concentrate on the closed scenario of more fences and quarantining Greece.

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Internal German government reports, according to the magazine Der Spiegel, predict a security and humanitarian emergency within days in Greece if it is cut off from the Schengen free-travel zone and refugees are stopped from continuing up the Balkans.

Greece remains in the line of fire because of its inability or reluctance to secure the maritime border with Turkey. It has been given three months by Brussels to improve its performance or face possible temporary eviction from Schengen.

The summit will warn Athens that failed or unregistered asylum-seekers entering Greece have to be returned immediately to Turkey.But Tusk, chairing the EU summit, spoke strongly on Tuesday against quarantining Greece.

Germany, Austria and others have reimposed partial national border controls in the Schengen area and want to retain the option to extend that to two years in May. In order to do so, Brussels has to rule that Schengen’s external borders are inadequately secured, meaning that Greece will be the scapegoat.

“There is no issue of isolating Greece,” said a senior EU official. “The external border is in Greece and will remain in Greece.”

Several countries, including the eastern European states, believe and hope that Merkel’s pact with Turkey will fail and that by the spring, when the refugee flows are almost certain to rise, their arguments will prevail. “Relying simply on Turkey to deliver is not enough,” said a senior eastern European diplomat. “Macedonia cannot cope with the flux.”

In a related development, the UK prime minister is to offer to send an official border force cutter vessel and maritime helicopters to join the Nato force that is being created to crack down on people smuggling in the eastern Mediterranean.

Amid fears that the Russian attacks on the Syrian city of Aleppo could lead to an increase in the numbers of Syrians seeking refuge in Europe, David Cameron will tell EU leaders that the UK is prepared to increase its contribution to the monitoring of people traffickers. He will tell EU leaders in Brussels that Britain is prepared to deploy its existing cutter vessel in the Mediterranean and to send an extra one to join a Nato standing maritime group.

Nato defence ministers discussed setting up the group, which is designed to focus on refugees crossing the Aegean from Turkey to Greece, at a meeting in Brussels last week. The plan is due to be adopted in the coming weeks.

The prime minister will also signal that he is prepared to deploy Merlin helicopters to the mission, and to assign liaison officers from the National Crime Agency to work directly with Turkish border guards. Turkey is a member of Nato.

The latest figures suggest that 2,000 refugees a day are arriving in Greece even during the winter months, with 60,000 arriving in January. More refugees arrived in the first four days of February than in the whole of the month last year.